1. Field of the Invention
The invention relates to a high speed data recording and reproducing apparatus for efficiently recording and reproducing a large amount of continuous data with a high data rate such as a moving image bit stream or the like to/from a plurality of disk devices arranged in parallel.
2. Description of the Related Art
Nowadays, use of an A/V server for recording what is called A/V (Audio/Video) data such as moving image data, audio data, and the like to a disk storage device such as a hard disk in place of a conventional tape medium is becoming wide spread. The A/V server ordinarily has a plurality of output channels and can independently output A/V data in parallel from the respective output channels. For example, in an A/V server which is used for transmission in a broadcasting station, A/V data of about 10 to 100 channels can be simultaneously outputted. In the A/V server, since a large amount of data is transferred at a high rate, for instance, a plurality of disk storage devices are connected in parallel and are used.
Hitherto, in order to control such a plurality of disk storage media, it is necessary to synchronize each disk storage device. As a method of synchronizing, either one of the following two methods has been used. The first method is a method whereby a reading or writing request is simultaneously sent to each disk storage device and the synchronization is obtained after the end of processes of all of the disk storage devices. The second method is a method whereby the rotation of a disk in each disk storage device is physically synchronized, thereby preventing a variation of performance in individual disk storage devices from occurring.
In the above methods, according to the first method, the time that is required by the A/V server in order to complete the reading/writing operation of data is equal to the time required by the disk storage device that finishes the individual processes last. On the other hand, an accessing time of each disk storage device depends on factors such as the rotation waiting time and the search time. Since those factors, however, differ for every device or process, they have a variation of a certain range. The first method, therefore, has a problem such that the accessing time of the whole server, which depends on the data rate, is longer than the average accessing time of each disk storage device of the server and, therefore, it is not efficient.
According to the second method, on the other hand, since physical factors such as an accessing time, etc. in each disk storage device constructing the server are identical, it is possible to expect that the accessing time of the whole server is almost equal to the average accessing time of each disk storage device. However, because special hardware is necessary as a disk storage device for this method there are problems such that the price is high and the usable storage capacity of the disk storage device is limited.
In the disk storage device, on the other hand, as a state where the accessing operation is most efficiently executed, a method whereby data is physically continuously arranged onto the disk storage device and the data is continuously accessed by a block size that is large to a certain extent without any disturbance is considered.
In order to continuously arrange a large amount of data, to implement this method however, the general OS (Operating System) cannot cope with such an arrangement and there is a problem that it is necessary to use a special OS. As mentioned above, in the A/V server, since it is necessary to output the data in parallel to a plurality of channels, there is also a problem that it is impossible to continuously access the data without any disturbance.